The present invention relates to a method and apparatus for the early detection and classification of retinal pathologies. More specifically, the present invention relates to a method and apparatus for early detection and identification of retinal pathology, including glaucoma and macular edema associated with diabetic retinopathy. In particular, the system of the present invention can be used to measure the relative amount of live fibers in a region of the Nerve Fiber Layer (hereinafter referred to as the xe2x80x9cNFLxe2x80x9d) of the retina to detect glaucoma at its very early stages, the opacification of the retina to detect edema, and changes in optic disk topography to detect the presence and/or progression of glaucoma.
Various retinal pathologies are known that can have moderate to severe effects on vision. Chief among them are glaucoma and edema associated with diabetic retinopathy. Glaucoma, characterized by nerve fiber loss (especially in the Nerve Fiber Layer of the retina) and ganglion cell loss, produces a progressive reduction in visual function beginning at the periphery of the field of vision and progressing inwardly to cause xe2x80x9ctunnel vision.xe2x80x9d If left untreated, it can lead to total blindness. Edema, a thickening of the retina (particularly in the macular region), results from leakage of blood vessels and causes a reduction in visual acuity. When a reduction in visual acuity occurs in a patient, it is up to the ophthalmologist to determine where the source of the problem is in the eye so that a suitable treatment can be planned. One way often used to test for the edema is by using flourescein angiography. However, this method is invasive, time-consuming, not quantitative, and the intensity of the fluouscence is not directly related to the edema.
The retina is both thin and transparent, and identification of problems in the retinal layers is difficult. In the case of glaucoma, changes in the retina have traditionally been able to be detected only after irreversible visual loss or damage has occurred. Considering that up to 50% of nerve fibers at a predetermined retinal region may be lost before a detectable vision problem occurs, it would be of significant advantage to be able to identify and quantify retinal changes before visual damage occurs. In particular, it would be of utmost benefit to be able to detect and quantify changes in the NFL (an indicator of glaucoma) and opacification of the retina (an indicator of edema) at a previously unattainable early stage.
One way ophthalmologists can diagnose glaucoma is through the use of Perimetry. Perimetry, however, detects only the functional irreversible damage in the retina that has already resulted in irreversible visual loss and does not detect the preceding physiological changes.
It is therefore the primary object of the present invention to provide a method and apparatus for the early detection and classification of retinal pathologies, including edema and glaucoma. Particularly, it is an object of the present invention to provide an apparatus and method for detecting retinal pathologies by determining and quantifying particular characteristics in the light scattering patterns of the different sublayers and regions of the retina. It is also an object of the present invention to provide an apparatus capable of precisely detecting retinal pathologies that is both noninvasive and capable of detecting problems before visual loss or damage occurs.
These and other objects of the present invention will become more apparent from the summary of the invention and detailed description of the drawings that follows.
The present invention relates to a method for early detection of retinal pathologies, especially glaucoma and diabetic macular edema. The method comprises the steps of: (a) illuminating a sequence of predetermined locations on the retina; (b) receiving light returning from said predetermined locations on the retina; (c) generating a series of primary graphs corresponding to the light intensity with respect to retinal depth of each of said predetermined locations on the retina; (d) separating the component curves of said primary graphs (one main component curve corresponds to light returning substantially from the Nerve Fiber Layer; a second main component curve corresponds to light returning substantially from the Retinal Pigment Epithelium); (e) analyzing said component curves (according to predetermined algorithms) to obtain data including, but not limited to, data corresponding to the front and/or back slopes and/or the area of at least one of the component curves; (f) comparing said data to analogous pre-specified data (to quantify changes and/or classify pathologies of the retina.)
In a preferred embodiment of the present invention, the method further includes the step of determining the retinal thickness for each of said predetermined locations of the retina, by employing, for example, the calculated distance between the component curves of the primary graph (it is appreciated that other approaches may be appropriately employed for determining retinal thickness.)
It should be appreciated that the sequence of predetermined locations on the retina need not be linearly spaced. Rather, said sequence of predetermined locations may refer to any particular region or area of the retina that may further be divided into sub-regions that are illuminated in a sequential manner (for a predetermined period) for the purpose of obtaining information about the light scattering pattern and/or changes in the light scattering pattern occurring over a region of the retina.
It should also be appreciated that separation of the component curves may be accomplished through any appropriate method such as by using curve-fitting methods including fitting a Lorenzian function of the primary graph and translating the Lorenzian to delineate a component curve corresponding substantially to the light returned from the Retinal Pigment Epithelium according to appropriate Lorenzian tables and, thereafter, subtracting the component curve corresponding to the Retinal Pigment Epithelium from the primary graph to obtain a second component curve corresponding substantially to the light returned from the NFL.
In accordance with a preferred embodiment of the present invention, the method further comprises the step of generating at least one three-dimensional map. Said map may correspond, for example, to the retinal thickness of the sequence of the predetermined locations of the retina. It is appreciated that a three-dimensional map may be generated corresponding to any one or more of the parameters measured (two dimensions corresponding to the position on the retina and one dimension corresponding to the measured parameter value). In one preferred embodiment, the method further comprises the step of generating at least one three-dimensional map representative of the relative amount of cells in the Nerve Fiber Layer of the retina over the sequence of predetermined locations on the retina (this map is preferably generated based on the calculated area of the component curves of the primary graphs that correspond to the NFL).
In further preferred embodiments of the present invention, the data is arranged in a matrix for enabling comparison with pre-specified data that is arranged in an analogous format.
In still further preferred embodiments of the present invention, the data corresponds to the area of the component curve that corresponds to the Nerve Fiber Layer of the retina.
Moreover in accordance with other preferred embodiments of the present invention, the data corresponds to the ratio of the area of the component curve corresponding to the Nerve Fiber Layer to the area of the component curve corresponding to the Retinal Pigment Epithelium.
In another preferred embodiment of the present invention, the data corresponds to the ratio of the area of component curve corresponding to the Nerve Fiber Layer to the area of the primary graph.
Moreover, in another preferred embodiment of the present invention, the data corresponds to differences between the Line Spread Function of the component curve corresponding to the Nerve Fiber Layer and the Line Spread Function of the component curve corresponding to the Retinal Pigment Epithelium. It is appreciated that a comparison between the two Line Spread Functions (LSF""s) may include calculation and comparison of a variety of different measurements. In one preferred embodiment, the back slope (i.e., the slope of the descending portion) of the component curve corresponding to the Retinal Pigment Epithelium is compared with the front slope (i.e., the slope of the ascending portion) of the component curve corresponding to the Nerve Fiber Layer.
In one preferred embodiment of the present invention, the pre-specified data is obtained from normal retinas. For example, if the region of the retina being illuminated includes the optic disk, the resultant data can be compared to data obtained from known normal (i.e., healthy) optic disks. In another preferred embodiment of the present invention, the pre-specified data is obtained from an earlier examination of the retina being examined. In another preferred embodiment of the present invention, the pre-specified data contains data obtained from known normal (i.e., healthy) optic disks and from an earlier examination of the retina being examined.
In a preferred embodiment of the present invention, the regions of the retina are illuminated successively according to a predetermined illumination sequence useful for the detection of a specific predetermined retinal region.
The present invention also relates to an apparatus for mapping the inner structure of the retina using the method hereinbefore described, that is especially useful for the early detection of retinal pathologies including glaucoma and diabetic macular edema. The apparatus comprises; (a) illuminating means for illuminating a sequence of predetermined locations on the retina and for receiving light returning from said predetermined locations on the retina; (b) computing means adapted to producing a series of primary graphs corresponding to the light intensity with respect to retinal depth of each of said predetermined locations of the retina, for resolving the component curves of said primary graphs, for analyzing the component curves to obtain data including data corresponding to the front and/or back slopes and/or the area of at least one of said component curves, and for comparing said data to analogous pre-specified data (to quantify changes and classify pathologies in the retina.)
It is appreciated that the illuminating means may be of any appropriate type known in the art for enabling production of optical cross section images from each location of the retina. For example, the illuminating means may comprise an instrument having a helium-neon laser, operating at a length of 543 nm, mounted on a slit-lamp biomicroscope. The expanded laser beam is directed toward the eye by a beam splitter and focused by the objective of the biomicroscope. The image of the intersection of the slit with the retina may be recorded on film via a second objective of the biomicroscope.